Method for generating heat energy and electrical energy from various types of waste and system for implementing said method

ABSTRACT

A method including obtaining biogas, treated water and oxygen from sewage and various wastes; feeding a boiler: in a first step, with biogas and oxygen, and in a second step, with treated water supplied at a very high pressure to the injectors of the boiler, while maintaining an input of biogas; producing superheated steam at a temperature above 650° C. and low humidity in a heat exchanger heated by the boiler; driving, by the produced steam, a steam turbine connected to an electric generator; and condensing the steam from the turbine and recirculating it to the heat exchanger.

OBJECT OF THE INVENTION

The present invention relates to a method for generating thermal and electric power from different wastes such as sewage, livestock wastes and in general waste from cities, industrial parks and/or farms, this method presenting some features aimed to achieve the production of thermal and electric power without generating toxic wastes and with minimum pollutant emissions to the environment. The invention further includes a system for implementing this method.

APPLICATION OF THE INVENTION This invention is applicable to facilities generating thermal and electric power from wastes. BACKGROUND OF THE INVENTION

The generation of electricity using energy from biomass and other combustible materials, such as municipal waste, presents, on one hand, limitations imposed on the steam generated in the boiler due to the corrosive nature of the flue gases, which become more corrosive the higher the temperatures, and on the other hand, the disadvantages of discharging polluting gases to the atmosphere.

Obtaining acceptable performance in such facilities requires a significant steam production and at an elevated temperature to power up the steam turbine in order to drive the power generator. In order to obtain this steam overheating, a boiler superheater is used, which is the component of the boiler reaching the highest temperatures and which is also subject to the above mentioned corrosion problems.

The document ES2010890 describes a system for power generation from the combustion of municipal solid wastes and the like comprising, in order to solve the problems discussed above, a first step of heating water in a solid waste incineration boiler, which operates below the temperatures at which undesirable corrosion problems appear in the elements of said boiler, and a second step of heating the steam obtained in the first step, performed by a boiler that reuses exhaust gases from one or more gas turbines, thus resulting, in the first step, saturated or slightly superheated steam at high pressure and, in the second step, the superheating or reheating of the steam obtained in the first step in conditions that are suitable for its application to a turbine steam.

This system has, on one hand, some obvious limitations due to corrosion problems both in the incineration boiler and in the recovery boiler due to the direct incineration of the solid wastes and, on the other hand, presents pollution problems because of the discharge of the combustion gases to the outside.

Therefore, the technical problem which arises is a method for generating thermal and electric power from different wastes that minimize the emission of pollutants to the outside and avoid the problems of corrosion caused by the direct combustion of wastes, as well as a system for the implementation of this method.

DESCRIPTION OF THE INVENTION

The method of generating thermal and electric power from various wastes object of this invention has constructive features aimed at preventing the direct combustion of wastes, using these wastes for obtaining combustible materials that are suitable for feeding a boiler and reaching therein a temperature above 1000° C. and a discharge of a minimum amount of pollutants to the atmosphere.

Another objective of the invention is the reuse of the generated steam after being used for driving a steam turbine connected to an electric power generator, said reuse being performed through subsequent condensation and return towards a heat exchanger located in the boiler.

To that end, and according to the invention, this method comprises the following steps or stages:

-   -   receiving sewage and different wastes with organic content         separately;     -   purifying the sewage by separating solid wastes contained         therein and processing the purified water to obtain treated         water;     -   obtaining hydrogen and oxygen from a portion of the treated         water through electrolysis treatment;     -   obtaining biogas by bio-digestion process of the organic         fraction of the various wastes and solid wastes separated from         the sewage;     -   feeding a boiler: in a first step, with biogas and oxygen         previously obtained from the wastes and the electrolysis         process, until reaching a temperature of 600° C.; and in a         second step, with treated water supplied at very high pressure         to the boiler nozzles, retaining a minimum input of biogas,         until reaching a temperature of 1200° C.;     -   producing superheated steam at a temperature above 650° C. and         low humidity in a heat exchanger heated by the boiler;     -   driving, by means of the steam produced, a steam turbine         connected to an electric generator;     -   condensing a certain volume of steam from the turbine and         recirculating it to the heat exchanger to be reused in a closed         circuit, and using the remaining steam from the turbine to raise         the temperature of the water at the entrance of the         electrolyser, and increasing the hydrogen production by         processing the biogas that has not been necessary to feed to the         boiler for proper operation.

This method allows generating thermal and electric power without generating toxic wastes of any kind.

For implementation of this method, the use of a system is provided that comprises a purifier for receiving the sewage and separating the solid wastes that are contained in said sewage.

Solid wastes separated from the sewage, along with the organic fraction from various other urban and/or industrial wastes are treated in a biodigester which provides: dry solid residue usable in various applications, and a biogas for feeding the boiler.

The purified waters from the purifier are processed in a treatment plant for obtaining treated water.

Part of the treated water is brought to an electrolyser wherein it is subjected to electrolysis and decomposed into hydrogen and oxygen; the oxygen being used for the boiler feed.

As mentioned above, the boiler is fed in a first step with biogas from the biodigester and the oxygen from electrolysis of the treated water, said boiler providing a temperature of 600° C.

Once this temperature is reached, a continuous biogas feeding is kept in a second step, and the feeding of a portion of the treated water at high pressure is performed by means of a feed and injection pump circuit to the injectors of the boiler. This injection of steamed water determines the combustion of the hydrogen of the injected water when the boiler is at a temperature above 590° C., while the boiler can reach a temperature of about 1200° C. in this second feeding step.

The boiler comprises exchangers which provide a high flow of superheated steam at a temperature above 650° C. and, having a low humidity, the thermal power of the steam is transformed into mechanical power which is used to drive a turbine, by rotating at first during the stages of high and medium pressure and finally during the stage of low pressure.

Part of the steam used to drive the turbine is brought to a large condenser and after the occurrence of the change of state, the water is returned again into the boiler exchangers to continue the cycle, the remaining steam being used in the production of a larger amount of hydrogen.

DESCRIPTION OF FIGURES

In order to complement the description that is being carried out and with the purpose of facilitating the understanding of the characteristics of the invention, the present description is accompanied by a set of drawings wherein, by way of a non-limiting example, the following has been represented:

FIG. 1 shows a schematic view of an exemplary embodiment of the system of the invention allowing for the implementation of the aforementioned generating method.

PREFERRED EMBODIMENT OF THE INVENTION

In the exemplary embodiment shown in FIG. 1, the system comprises a purifier (1) in which sewage (AR) is received and the solid wastes are separated and brought to a biodigester (2) and liquid wastes are brought to a treatment plant (3).

The treatment in the biodigester (2) of the separated solid wastes, along with the organic fraction from various other wastes (RD) from urban and/or industrial origin, provides, on one hand, a dry solid waste that is transferred to a warehouse (21) for later use in various applications and, on the other hand, a biogas which is gathered in storage tanks (22) and is then used in the feeding of a boiler (4); the exceeding biogas having the possibility of being used in any other applications, for example to heat the biodigester.

In the treatment plant (3) the liquid wastes are subjected to a filtering process, hardness reduction and removal of suspended solids, for example, by using colloidal suspensions, to obtain treated water.

A portion of the treated water is brought to the electrolyser (5) where hydrogen and oxygen are obtained by electrolysis. Oxygen can be bottled, employed in the process of treating sewage or used for feeding the boiler (4); with the oxygen being transported into a gaseous state to an injection pump block (6) to which a portion of the treated water from the treatment plant (3) enters through a separate duct of the water.

In an initial or starting step, the boiler (4) is fed with oxygen and biogas until reaching a temperature of about 600° C., then going on to a second step in which the treated water is supplied at a very high pressure through the pump group (6) to the boiler injectors, what allows to reach a temperature of about 1200° C. by maintaining a constant feeding of biogas.

The heat exchanger (7) of the boiler provides a high flow of superheated steam at a temperature above 650° C. and low humidity. This steam is used to drive a steam turbine (8) connected to the shaft of an electric generator (9).

Part of the steam used for driving the turbine (8) passes through a condenser (10) where the change of state of the steam is produced, the water being returned to the heat exchanger to repeat the operation cycle, injecting water at the pressure required to keep the production of superheated steam stable throughout.

As can be seen in the attached figure, inside the condenser (10) a second heat exchanger (11) is arranged, which, by means of the movement of a fluid, cools a portion of the steam to achieve its condensation and the uptake of steam thermal power for being used in any other equipment or process.

Once the nature of the invention as well as an example of preferred embodiment have been sufficiently described, it is stated for all pertinent purposes that the materials, form, size and arrangement of the elements described are susceptible to changes, provided these do not involve an alteration of the essential characteristics of the invention that are claimed subsequently. 

1. A method for generating thermal and electrical power from different wastes of the type comprising the use of a boiler to produce steam and feed said steam to a steam turbine that is connected to a generator: characterized in that it comprises: receiving sewage (AR) and various domestic and/or industrial wastes (RD) separately; purifying the sewage by separating solid wastes contained therein and processing the purified water to obtain treated water; obtaining hydrogen and oxygen from a portion of the treated water through an electrolysis process; obtaining biogas by a bio-digestion process of the organic fraction of the various wastes and from the solid wastes separated from the sewage; feeding a boiler: in a first step, with biogas and oxygen previously obtained from the wastes and the electrolysis process, until reaching a temperature of 600° C.; and in a second step, with treated water supplied at very high pressure to the boiler nozzles, retaining a minimum input of biogas, until reaching a temperature of 1200° C. producing superheated steam at a temperature above 650° C. and low humidity in a heat exchanger heated by the boiler; driving, by means of the steam produced, a steam turbine connected to an electric generator; condensing a certain volume of steam from the turbine and recirculating it to the heat exchanger to reuse it in a closed circuit, using the remaining steam from the turbine to raise the temperature of the water at the entrance of the electrolyser; and increasing the hydrogen production by processing the biogas that has not been necessary to input to the boiler for proper operation.
 2. Method according to claim 1, characterized in that it comprises the liquefaction and the storage in cryogenic tanks of the hydrogen obtained in the process of electrolysis of the treated water.
 3. System for implementing the method of claim 1, characterized in that it comprises: a purifier (1) for receiving sewage (AR) and separating the solid wastes contained therein from the liquid wastes; a biodigester (2) for the treatment of the separated solid wastes, together with the organic fraction of various other urban and/or industrial wastes (RD), and obtaining a dry solid residue and a biogas; a treatment plant (3) for the processing of the purified water from the purified water and the obtaining of treated water; an electrolyser (5) where hydrogen and oxygen are obtained by electrolysis from a portion of the treated water, a boiler (4) provided with an injection pump block (6) for the supply of oxygen, together with biogas in the first step of the boiler feed, and the supply of purified water at high pressure in the second step of the boiler feed by keeping a constant supply of biogas ; a heat exchanger (7) to generate superheated steam intended to drive a steam turbine (8) connected to the shaft of an electric generator (9); and a condenser (10) for condensing a portion of the steam from the turbine and returning it to the heat exchanger (7). 